The invention relates to catheters in general, and more particularly to improvements in dilatation or expansion catheters which need not employ one or more inflatable and deflatable balloons. Still more particularly, the invention relates to improvements in dilatation catheters of the type wherein a mechanical dilator or expander is to be introduced into a selected portion of an internal passage or cavity in an animal body to act upon the tissue surrounding the selected portion of such passage or cavity (hereinafter called passage for short). By way of example, the catheter of the present invention can be utilized to dilate a constricted portion of a blood vessel.
U.S. Pat. No. 3,557,794 discloses a catheter wherein the expander or dilator comprises a set of leaf springs. A wire is attached to the ends of such springs and can be manipulated to change the shape of the springs by causing them to bulge outwardly and to thus expand a portion of an internal passage. A drawback of the patented catheter is that the expanding action of the leaf springs is neither predictable nor uniform because the extent of deformation (bulging, arching or bending) of each spring varies in the longitudinal direction of the expander. Thus, it can happen that the radially outermost portions of the deformed leaf springs bring about an excessive expansion of the corresponding portion of an internal passage but the immediately adjacent portions of such passage are subjected to a much less pronounced (and normally much less satisfactory) expanding action or no dilatation at all.
Attempts to overcome the drawbacks of the patented catheter include the utilization of catheters which employ inflatable balloons. For example if the inflated balloon at the distal end of a balloon-introducing sheath assumes a substantially cylindrical shape, it is capable of effecting a more or less uniform expansion of tissue surrounding a selected portion of an internal passage, such as that defined by a blood vessel. However, balloon catheters exhibit the drawback that, as long as the balloons are inflated, they normally or invariably prevent the flow of a body fluid through the expanded portion of a blood vessel or the like. Presently known attempts to avoid the just outlined drawbacks of balloon catheters contribute significantly to their cost but do not invariably ensure an uninterrupted flow of blood and/or another fluid through the balloon-dilated portion of an internal passage.
Cardiologists and radiologists are frequently required to ensure that a selected portion of an internal passage remains open (unobstructed), at least for a certain interval of time. For example, such temporary preventing of obstruction (i.e., temporary retention of a selected portion of an internal passage in a fully or at least adequately expanded condition) is often necessary in order to prevent spasmodic contraction of an artery during balloon angioplasty. Thus, at least under certain circumstances, the artery must be maintained in an expanded condition during angioplasty in order to prevent certain parts of the intima from causing or entailing contraction of the artery not unlike the closing of a valve. Such spasmodic contraction can be remedied or counteracted only by resorting to undertakings as drastic as bypass surgery. This can be avoided by reliably ensuring an at least temporary flow of blood to various parts of an animal body, e.g., to certain vessels of the heart, at a required or optimum rate.
Furthermore, a satisfatory carrying out of angioplasty often necessitates or renders it desirable to subject the tissue surrounding a selected portion of an internal passage to a particular treatment subsequent to completion of balloon dilatation; this reduces the risk of renewed stenosis.